XHTML is
NOT the "latest" version of HTML, it is
NOT a replacement for HTML, it will
NEVER replace HTML.
HTML 5 will be the replacement for HTML 4.01 when it gets beyond a working group draft document
XHTML is a designed to be used with XML, so strictly speaking, unless you are using XML/XSLT on your pages you should be using and validating to a HTML 4.01 Strict doctype.
target="" IS perfectly valid in XHTML as well, but only in the doctype where it actually has any meaning, and that is a frameset DTD.
In actual fact, a frameset DTD has
always been the only one where target="" is valid, because without a frameset the target attribute has no meaning.
The mere fact that it worked does not make it correct to use